One of the major problems in mobile telephone systems with packet data transmission in the uplink is how to divide the access resources to different users when the need for resources varies between users at a given point in time.
In current systems, each user is reserved a certain amount of capacity and base station hardware resources during a circuit-switched call for as long as communication capability is needed. However, when using circuit-switched transmission of packet data in this way wherein data to be transmitted is typically very bursty in nature, it is a waste of radio capacity and physical hardware resources to keep a single user's connection reserved all the time according to the greatest possible momentary data transmission need. Thus, packet-switched transmission of packet data is preferable, but having the connection totally disconnected between data transmissions can mean a lengthy process with a lot of signaling via the Random Access Channel (RACH) every time there is data to be transmitted.
In systems based on the code division multiple access (CDMA) method, different users use different uplink scrambling codes. When initiating transmission in a CDMA system, a big concern is how to ensure that the access takes place fast without a lot of signaling via RACH. Also, for longer packets, a major concern is how to take care of power-control to avoid the near-far problem typical of the non-orthogonal coding used in CDMA technology, in order to ensure that user equipment near to a radio network subsystem or base station will not exchange signals at unnecessarily high power compared to different user equipment farther away.
In the current types of systems, the uplink services have not been packet based, or they have been implemented with a circuit switched connection. Also, for some of the services like short message service (SMS), the data amount has been very small. In future systems, the applications are expected to have a larger range, from database applications, to email and internet browsing, to any other TCP/IP traffic, and consequently the current types of systems are not acceptable.
In the downlink, the power control problem is not that severe and, in existing CDMA systems like IS-95A, a downlink power control is not provided at all. In the downlink direction, a greater emphasis is put on sharing the physical resources efficiently, as has been done for example with a downlink shared channel in wideband CDMA (i.e. WCDMA also known as UMTS).
In the UMTS system, the concept of an Uplink Common Packet Channel (Uplink CPCH) has been proposed to solve the uplink access problem. CPCH also has significant advantages for data transmission. However, Uplink CPCH suffers from a reliability problem. Using Uplink CPCH, the proposed channel allocation procedures may lead to two or more user equipments transmitting their data on the same CPCH channel and thus causing excessive interference. Access to a CPCH channel takes time, and thus a channel selected by a first UE may be reserved by a second UE before the first UE completes the access process. In other words, user channel selection (UCS) proceeds by the user selecting and accessing a free CPCH channel according to the description of free channels sent to the UE over a broadcast channel (BCH); however, the delay in the access method and in the BCH transmission may cause UE to access a channel which is already reserved.
Another attempted solution to the uplink access problem has been to use versatile channel assignment (VCAM), where the channel is assigned, after access preambles are exchanged, by way of an acquisition indication channel (AICH). The problem with this related art technique is that AICH typically has an error rate in the range of one percent (1%). VCAM, however, requires reliable signaling, and therefore the high AICH error rate often will cause two UEs to transmit into the same CPCH. The UEs consequently would follow a single power-control stream, often causing severe noise levels at the receiver.
The basic CPCH structure discussed here is based on 3rd Generation Partnership Project (3GPP) specifications available to the public. 3G TS 25.211 “Physical channels and mapping of transport channels onto physical channels (FDD)” (Version 3.1.1, December 1999) describes the characteristics of transport channels and physical channels in the frequency division duplex (FDD) mode of UMTS terrestrial radio access (UTRA). 3G TS 25.212 “Multiplexing and channel coding (FDD)” (Version 3.1.1, December 1999) describes the characteristics of multiplexing and channel coding in the FDD mode of UTRA. 3G TS 25.213 “Spreading and Modulation (FDD)” (Version 3.1.1, December 1999) describes spreading and modulation in the FDD mode of UTRA. 3G TS 25.214 “Physical Layer Procedures (FDD)” (Version 3.1.1, 12/1999) specifies and establishes the characteristics of the physical layer procedures in the FDD mode of UTRA. Further, the 3GPP TSG RAN WG1 submission 3GPP R1-00-0175 describes the basic monitoring channel structure (this document is dated Jan. 18–21, 2000).
Submission 3GPP R1-00-0175 is a useful example to understand the background of the present invention, and especially section 5.3.3.8 of that submission, which describes a CPCH status indication channel (CSICH). Likewise, 3G TS 25.214 contains a relevant section 6.2 entitled “CPCH Access Procedures.” That section 6.2 lists relevant physical layer parameters; the 18-step access procedure described in section 6.2 is improved by the present invention in order to address the prior art problems discussed above.